Wide World of Weeds III

Ron Strahan

Weed Basics

What is a Weed?

A plant growing out

of place

A plant whose

virtues have not yet

been discovered

Some reasons weeds are

problems?1) Reduce yields of crops – harvest efficiency

2) Reduce land use efficiency

3) Spoil beauty of turf and ornamental areas

4) Diminish enjoyment of outdoor recreation

5) Can cause allergic reactions due to toxicity

Weeds are great competitors!

• Water

• Nutrients

• Light

Why so many weeds? – Pigweed

example

13,000 – 100,000 seed/year

Dormancy – survive 30 years

Don’t allow seed production

How are weeds able to persist?

1) Number of seed produced

2) Survival of weed seed

3) Dormancy

4) Vegetative reproduction

How do weeds spread?

1) Nature

Animals and birds – Chinese tallow tree

Winds – dandelion

Rains and flooding

Some type of runner – rhizome, stolon

2) Humans

Impure seed/sod – contaminated wildflower

Compost and mulch – animal droppings

Irrigation – wet areas for sedges

Machinery – contaminated mowing equipment

Contaminated soil

Types of Weeds• Broadleaves –

– Netted veination

– 2 cotyledons

– Taproot

– Showy flowers

• Grasses –– Parallel

– 1 cotyledon

– Fibrous roots

• Sedges –“nutgrass”

– Triangular stems

– Leaves in 3’s

Virginia

buttonweed

Crabgrass

purple nutsedge

Annuals?

Perennials?

Types of Weeds

• Annual and perennial summer weeds

• Annual and perennial winter weeds

Goosegrass (a) Virginia buttonweed (p)

Burweed (a)

Crabgrass (a)

Annual

bluegrass (a) dandelion (p)

Mismanagement

causes

Lots of weeds in the

lawn

Weed Control in Lawns

Most important concept in weed control

is proper turfgrass management

Thin Turf = Weedy Turf

Indicator Weeds

Soil condition Indicator weeds

soil compaction

goosegrass, Poa

low nitrogen clovers

poor drainage

Dollarweed, sedges,

doveweed

drought Dallisgrass, bahiagrass

Weed Control in Lawns

• Before you spray a herbicide – you need a basic knowledge of lawns and weeds

• Improper applications can be very costly

• Spray wrong herbicide on turf

• Equipment not calibrated

• Did not read label

Understand

Turfgrass Basics

Choosing the right turfgrass

species

• Purpose of turf – plans for area

• Match grass with growing area

– Shade

– Soil type

– Traffic

– High maintenance vs. low maintenance

Turfgrasses for Louisiana Lawns

St. Augustinegrass

Centipedegrass Bermudagrass

Zoysiagrass

Basic Lawn

Knowledge Needed

Because….

½ of Weed Control

is

Maintaining turf

properly!

Practices that improve turf

Discourage competition

from weeds

Proper Management First

• Choose the right grass species

• Mowing and fertilizing

• Traffic control

• Control diseases and insects that weaken

turf

• Applying irrigation properly

Control Diseases and Insects

Cultural practices that

improve turf or crop stands

Discourage competition

from weeds

Lawns are not golf

greens!

Don’t Mow so

Low!!!!!

Mower Deck – Can be an

enemy to lawn

Mowing Heights

• St. Augustinegrass - 3”

• Zoysiagrass - 1 to 2”

• Centipedegrass - 1 1/2 to 2”

• Bermudagrass - 3/4 to 1.5”

Chronic weed problems

Symptoms of poor

management!

Methods of Weed

Control

Options for Weed Control

• Encouraging turf/crop growth

• Mowing

• Hand pulling/hoeing

Herbicides

Brief Herbicide School

Session

What is a herbicide?

A chemical which injures or kills a plant.

Definitions

• Active ingredient – molecule that

provides herbicidal action

– Glyphosate – Roundup, Eraser etc

– Trifluralin – Preen, Treflan

• Mode of action – physiological process

that leads to negative plant effects

– Photosynthesis inhibitor - Atrazine

– Mitosis disruptor – Preen

– Amino acid production disrupted - Roundup

Preemergence?

Postemergence?

Types of Herbicides

• Preemergence – Weed preventor/residual

herbicides – controls weeds before you

see them

• Postemergence – kills weeds that are

actively growing

Preemergence

Herbicide Information

Effective Preemergence

Application

• Apply before weeds germinate

• Adequate rainfall or irrigation is needed

• Do not expect all season control - reapply

How do preemergence

herbicides work?

Herbicides provide a barrier

at or just below soil surface

How Do Preemergence

Herbicides Work?

When Should I Apply

Preemergence Herbicides

in My Yard?

Crabgrass

• Summer annual

• Produces lots of seed

• Germinates - soils reach 53 - 58F

• Light is required for germination

Goosegrass

• Summer annual

• Produces lots of seed

• Germinates - soils reach 60-65F

• Light is required for germination

When to apply preemergence

herbicide in turf

• Summer Weed Control- Around March 1 in North LA

Scotts Halts

Green Light Crabgrass Preventer

Hi Yield with Dimension

• Winter Preemergence – apply toward the end of September or early October

Postemergence

Herbicides

Types of Herbicides

• Nonselective – kills everything -

Roundup, Finale

• Selective – controls certain plants and

releases other species – Weed-B-Gone,

Vantage, Atrazine

What determines selectivity?

• Time of application

• Rate of application

• Chemical, biochemical, morphological or

physiological differences

Knowledge of when and how to use

herbicides

Types of Herbicides

• Contact – burns back what only what it

hits - Diquat, Finale

• Translocating (systemic) – move

throughout plant – Weed-B-Gone,

Vantage, Roundup

Roundup

• Active ingredient – glyphosate

• Will kill or injure most plants

• A systemic herbicide – good on perennial weeds

• Totally deactivated when it hits soil

• Visual symptoms in 2-4 days in growing points

• Find everywhere

Weed B Gon

• Ortho

• 3 way herbicides

• Low % of 2,4-D

• Excellent for winter broadleaves

Homeowner Weed Killers

Postemergence Facts

• Easier to control small actively growing weeds

• Some temporary injury to turf

• Greater turf injury at high temps (> 85F)

• Few options for St. Augustinegrass - very injury

prone

Very Injury Prone

St. Augustine is the Sissy of all

Turfgrasses

Bad Times to Apply Herbicides

1) Transition periods for lawns

2) Drought stressed periods

3) Newly sodded, sprigged, or seeded turf

4) Increased injury to turf when temps are above 85 F – some herbicides are volatile

5) When you did not read the label

Read the Label!

Before you apply a Herbicide

What’s on Label

1) Type of formulation – L, DG, WP, DF

2) Use classification – general use vs restricted

use

3) Common and chemical name

4) Precautionary statements

Proper Pesticide Use

1) Read label – label tells how to use and precautions

2) Store properly

3) Never eat or smoke near chemicals

4) Wear protective clothing

5) Use correct rate (calibrate)

6) Avoid drift and water contamination

7) Triple rinse containers

IPM

Takes into account all disciplines that affect

plant health

Make treatments when pest reach

unacceptable levels – monitoring is necessary

Object – not to eliminate pest but keep

populations below damaging levels

Pesticides and the

Environment

Master Gardeners have a unique

opportunity to educate others about

proper pesticide use and the environment

Reducing plant stresses reduces pesticide

loads on the environment

Flowerbed Weed

Management

Preemergence herbicides

– tremendous tools for flowerbeds

Steps Applying Preen/Amaze etc. –

Existing Bed

1. Remove existing weeds by hand

2. Sprinkle granules as directed over

existing landscape plants and on top

of old mulch – water in

3. Do not expect all season control -

reapply

Steps for Pre application – new bed

1. Prepare flower bed

2. Transplant landscape plants and water

3. Sprinkle herbicide granules as directed

over new landscape plants – rinse off

4. Apply mulch

5. Do not expect all season control - reapply

Consumer Preemergence

Herbicides for Flowerbeds

• Preen – active ingredient is dithiopyr now

• Amaze – benefin + oryzalin

• Hi-Yield with Dimension – dithiopyr

Work extremely well and very safe

Preemergence Herbicides – great

on…..

• spurge

• Purslane

• Pigweed

Preemergence Herbicides – Will

not work on …..

• Bermudagrass

• Torpedograss

• Florida Betony

• Chamberbitter

Chamberbitter

• Summer annual

• Vietnam

• Reproduces by seed

• Each fruit contain 6 seeds

• Very common in flower beds

Chamberbitter – what do you do?

• Light is needed for germination

• Add thick mulch in March

• Keep it hand pulled

Florida Betony – not controlled

by preemergence herbicides

Rattlesnake Weed

Florida Betony Staychis floridana

• Perennial plant

• Square stem

• White to pink flowers

• Reproduces quickly by tubers

• Smells like an ashtray

Control? Florida Betony Staychis floridana

• No selective post control in landscapes

• No preemergence

• Weed fabric not effective

• Non-selective herbicides

• WIPE with Roundup

• Apply Bobcat

Bobcat Treatment

Grass Control in

Landscape Beds

Did you know that you don’t have to hand pull

bermudagrass!!!!

You can control bermudagrass

in landscapes!

Control Grasses in the flowerbed

• Vantage - sethoxydim -

• Hi-Yield Grass Killer- sethoxydim – up to 3 oz/gallon – can be used in vegetable gardens

• Ferti-lome Over the Top II – is now sethoxydim – also can be used in vegetable gardens

• Grass B Gon RTU – same as Fusilade – ready to use

These herbicides work well on most summer grasses except……

Torpedograss!!!!

Torpedograss!!!!

Nutsedge (nutgrass or coco)

Purple Nutsedge

Produces

chains of

tubers

Image• Pretty good on sedges (nutgrass)

• Active ingredient – imazaquin

• 3.75 oz/gallon

• Dollarweed – very slow

• Landscape uses

• Safe on all warm season turf

• Image has become a brand –use the imazaquin active ingredient

Sedgehammer (halosulfuron)

• Also called Monterey Sedge Killer

• Purple and yellow nutsedge

• Safe on all warm season turf

• Available in consumer packets for 1 gallon of spray material

• May be applied around woody ornamentals

Sedge Control in Lawns and

Landscape

• Sedgehammer Herbicide - Best sedge activity available to homeowners – safe for the lawn

• Sedgehammer Herbicide - can be applied around woody ornamentals

• Image Herbicide- Good on sedges plus some broadleaf activity – several tolerant ornamentals in landscape beds – safe for the lawn

• Indian Hawthorne, gardenia, asiatic/confederate jasmine

Holly (several), Juniper (several), red crape myrtle, liriope, mondo, Hosta

Lawn Weed Control

Weeds in your Yard in

February

and March

Winter Weeds !

Winter Broadleaves

• Bedstraw

• Black medic

• Common

chickweed

• Henbit

• White clover

• Lawn burweed

Broadleaf Weed Killers – For Homeowners

• 2,4-D, Mecoprop, Dicamba

• Watch the hot weather on St. Aug – spot treat

• Don’t expect Virginia buttonweed control

• Excellent on winter broadleaves

2,4-D

• Broadleaf weeds only

• Can be tough on Centipedegrass and St. Augustinegrass – very tough in hot weather

• Watch out for tomato and okra – very sensitive

• Fair on buttonweed

• Poor on mature lawn burweed (sticker weed) and white clover

Weed B Gon

• Ortho

• 3 way herbicides

• Easiest on turfgrass – go with this one if it is 90F

• Low % of 2,4-D

• Excellent for winter broadleaves

Weed Free Zone

• Ferti-lome

• 3 way plus carfentrazone

• Decent St. Aug tolerance

• Available at nurseries and feed stores

• Same strength as professional Speedzone

Atrazine consistently out-

performs other herbicides on

winter weeds

*Safe for St. Augustinegrass, centipedegrass, zoysiagrass

and dormant bermudagrass

*Be careful with newly planted shrubs – less issues with

established trees

Lawn Burweed – sticker weed

•Treat in February and

March

•Too late in April and

May

•Atrazine, Weed B

Gon, Weed Free

Zone

How many times have I seen this?

Clover – indicator weed

Indicates low Nitrogen fertility

Clover Options

• Atrazine is unbeatable for winter weed control

• Weed B Gon

• Bayer Broadleaf Weed Killer – St.

Augustinegrass Formula

• Ferti-lome Weed Free Zone

Dollarweed

Dollarweed

• Perennial

• Indicates wet areas

• Reproduces by seed

and rhizomes

1. Atrazine

2. Weed Stop 2X

3. Ortho Weed B Gon

4. Ferti-lome Weed Free

Zone

5. Scott’s Bonus S – Weed

& Feed

Weed and Feed

• Careful around flower beds shrubs

• Don’t always perform well in our experiments

• Prefer addressing fertilizer/weed problem

separately

• Late-March to April timing

Grassy weed control in

centipedegrass and St.

Augustinegrass

Grassy weed control in

centipedegrass

Vantage / Poast or Hi-Yield Grass Killer

• Sethoxydim – active ingredient

• Use in Centipedegrass only – no other southern turf is tolerant

• Good on bermudagrass

• 1 oz per gallon but centipede will tolerate higher

• Annual bluegrass not controlled

Torpedograss Suppression in

Centipedegrass

Latest LSU Research – 3 applications of

Vantage (sethoxydim) spaced 28 days

apart - suppression

No good option for grassy

weed control in St.

Augustinegrass

Serious Summer Weed

Problems in Lawns

Virginia Buttonweed

Virginia Buttonweed

Virginia Buttonweed

• Tolerates low mowing

• Highest seed germ

at 86 F - July

• Reproduces by seed – 2 seed in every capsule (above/below ground)

+ stem fragments etc.

• Number 1 weed in South

Weed Free Zone

• Ferti-lome

• 4 way herbicide that contains carfentrazone

• Decent St. Aug tolerance

• Same strength as professional Speedzone

• Decent but not great VBW control – 2 applications needed

• Rate = 1.5 oz/gallon

VBW Consumer Herbicides

1. Manor – 80%

2. Weedfree Zone – 60% - 2 shots are needed for long term control

3. Weed Stop 2X – 45%

4. Weed B Gon – 40%

5. Weed B Gon Max – 35%

6. Bayer Southern – 30%

7. Southern Ag Trimec – 30%

Dallisgrass

Dallisgrass

• Perennial - stubby rhizomes

• Common throughout the south

• Tolerates low mowing and drought

• Fairly cold tolerant

Dallisgrass Control

• Vantage –

centipedegrass

• MSMA – now very

limited use

bermudagrass

• Roundup – St.

Augustinegrass

Brush and Briar Control

Best Brush Killers – contain triclopyr

• Ortho Poison Ivy and Brush Killer, Hi-Yield , Bayer Brush Killer – contains about 8% triclopyr

– Briars

– Woody plants

– Usually 4 to 8 oz per gallon of water

• Triclopyr - be careful with woody roots

– Can be absorbed by bark on trunks!!!

Poison Ivy

• Perennial

• Reproduces by seed

• Has some look-a- likes

• Roundup, Brush-B-

Gone, Greenlight Cut

vine and stump killer

Fingers 3 turn and flee…..fingers 5 let it thrive

Greenlight Cut-vine and Stump Killer or

some other version of (triclopyr)

Use Triclopyr for unwanted trees and vines with the cut

stump method (Greenlight Cut-vine and Stump Killer or Brush B Gon)

Cut unwanted vine or tree with loppers and treat fresh cut with triclopyr

Roundup-glyphosate

information

Glyphosate with 41% active

• Roundup, Hi-Yield Killzall, Eraser, Eliminator etc.

• Will kill or injure most plants

• A systemic herbicide – good on perennial weeds

• Totally deactivated when it hits soil

• Visual symptoms in 2-4 days in growing points

Roundup Brands

• 18%, 41%, 50% glyphosate

• Ready to use products also – usually < 2%

• Roundup Extended – Contains diquat and imazapic – Around trees

– Patios – bricks and driveways, gravel areas

– Do not spray in flower beds

• Prone to drift with high pressure and windy conditions

Azaleas are sensitive to

Roundup/glyphosate drift

Weed Wipers on the market

Rubber/Cotton Glove

Method

Rubber Glove/Cotton Glove

• 4 oz glyphosate in 32 oz water

• Rubber glove inside cotton glove

• Dip and squeeze off excess

• Use ungloved hand to remove desirable foliage

• Gently wipe weed leaves

Organic Weed Control

Perfectly Natural - Organic

• 90% vinegar and 8% clove oil

• RTU – no mixing

• Smells good

• Tried it – works well on small annuals

Preen Organic Corn Gluten

• 100% granulated corn gluten meal

• Apply 5 lbs. per 250 sq. ft. (25' x 10') to flower bed

• gluten releases an enzyme that interferes with germinating seeds

• Gave fairly good weed control for 20 days in an experiment

What can I do right now?

• Carefully spot apply broadleaf killer to lawn

• Clean out flower beds and apply Preen, Amaze,

etc.

• Spot treat with Roundup

• Kill vines with cut stem treatment

Questions ?